Hepatitis C virus (HCV) infection is a major worldwide health problem. Approximately 170 million individuals worldwide are infected by HCV and chronically infected patients carry a high risk of developing cirrhosis and hepatocellular carcinoma (Cohen 1999 Science 285:26–30).
Interferon-α either alone or in combination with ribavirin is used for therapy of HCV showing efficacy in between 20% and 40% of patients respectively.
HCV is an enveloped virus the genetic information for which is encoded in a 9.5 kilo bases positive strand RNA genome. A highly conserved noncoding region of 341 base pairs is localized at the 5′-end of this viral genome, which is followed by a long open-reading frame coding for a polyprotein of approximately 3,010 amino acids. Two putative envelope glycoproteins, E1 (gp35) and E2 (gp72) have been identified with 5 or 6 and 11 N-linked glycosylation sites, respectively. A high level of genetic variability is associated with the envelope genes. This is highly accentuates at the 5′-end of the E2 gene, where two hypervariable regions termed HVR1 and HVR2, have been described (Kato et al., 1992 Bioch. Biophys. Res. Commun. 189:119–127).
Studies using HCV E1–E2 proteins expressed in mammalian cells showed that infected individuals have an antibody response to HCV E2 (Harada, et al., 1994 J. Gen. Virol. 76:1223–1231). Recent work proposes the existence of neutralizing antibodies in serum from HCV infected patients (Rosa et al., 1996 PNAS (USA) 93:1759–1763; Zibert et al., 1995 Virology 208:653–661; Zibert et al., 1997 J. Virol. 71: 4123–4127).
Investigators employed surrogate assays to provide insights into virus neutralization since the virus cannot be grown in vitro (Houghton. Hepatitis C viruses. In Fields B N, Knipe D M, Howley P M (eds) Virology. Lippincott-Raven, Philadelphia, pp1035–1053). One surrogate assay, the neutralization of binding (NOB) assay, evaluates the ability of a given antibody or serum to prevent the association of HCV E2 protein with a human T-cell line (Rosa et al., 1996 PNAS (USA) 93:1759–1763).
Habersetzer et al., 1998 Virology 249:3241 describes human monoclonal antibodies capable of inhibiting the interaction of HCV E2 with human cells in vitro. Burioni et al., 1998 Hepatology 28:810–814 report human recombinant Fabs for the HCV E2 protein similarly capable of inhibiting the interaction of HCV with human cells in vitro.
PCT patent application WO 200005266 discloses antibodies comprising at least one complementarity determining region (CDR) of the variable domain of a human antibody that specifically recognize a conformation-dependent epitope of HCV E2 and are capable of precipitating E1/E2 complexes.
PCT patent application WO 9740176 discloses a recombinant human antibody Fab portion capable of binding to HCV E2 obtained using a combinatorial antibody library. The relevance of such antibodies for therapy of HCV infection still needs to be demonstrated.
It is therefore of substantial interest to identify human monoclonal antibodies (Mabs) directed against the E2 glycoprotein that are capable of neutralizing HCV infection in vivo. Such antibodies may constitute a new alternative for the treatment of HCV infections.
Cardoso et al., J. Med. Virol. 55, 28–34 (1998) describes the isolation of human monoclonal antibodies capable of binding to hepatitis C virus envelope glycoproteins. One of the described antibodies (4F7) was further characterized and sequenced and is the subject matter of the present invention.